The present invention relates to an air conditioning apparatus mounted on cars, and is particularly concerned with a car air conditioning apparatus using an engine as power source and a controlling method therefor.
A prior art air conditioning apparatus mounted on a car having a main engine as the power source for driving, for example, a diesel car, bus or other vehicle comprises an open type compressor unit driven directly by the main engine, a condenser connected to the compressor unit, an expansion means, an evaporator, a condenser blower, an evaporator blower and other components. Then, for adjusting the capacity according to fluctuation in an air conditioning load, a clutch provided for power transmission between the main engine and the compressor is controlled intermittently, or a displacement of the compressor is changed. The apparatus of having been disclosed in Japanese Patent Laid-Open No. 59-109423 is known well as representing the prior art air conditioning apparatus described above.
Meanwhile, the main engine speed sharply changes according to a travelling state of the car itself. Concretely, the speed changes between 600 rpm and 1,800 rpm or so. Accordingly, a speed of the compressor driven directly by the main engine sharply fluctuates likewise as in the case of the main engine. Consequently, in the air conditioning apparatus having a refrigerant in a cycle circulated by the compressor, the capacity changes between 33% and 100%. Thus, in the prior art air conditioning apparatus, the air conditioning capacity sharply fluctuates, and a careful consideration cannot be given to a requirement for securing steady cooling capacity.